THE STORY OF ELECTRICITY
BY JOHN MUNRO
AUTHOR OF ELECTRICITY AND ITS
USES, PIONEERS OF ELECTRICITY,
HEROES OF THE TELEGRAPH, ETC., AND
JOINT AUTHOR OF MUNRO AND
JAMIESON'S POCKET-BOOK OF
ELECTRICAL RULES AND TABLES PREFACE.

A work on electricity needs little recommendation to stimulate the
interest of the general reader. Electricity in its manifold
applications is so large a factor in the comfort and convenience
of our daily life, so essential to the industrial organization
which embraces every dweller in a civilized land, so important in
the development and extension of civilization itself, that a
knowledge of its principles and the means through which they are
directed to the service of mankind should be a part of the mental
equipment of everyone who pretends to education in its truest
sense. Let anyone stop to consider how he individually would be
affected if all electrical service were suddenly to cease, and he
cannot fail to appreciate the claims of electricity to attentive
study.
The purpose of this little book is to present the essential facts
of electrical science in a popular and interesting way, as befits
the scheme of the series to which it belongs. Electrical phenomena
have been observed since the first man viewed one of the most
spectacular and magnificent of them all in the thunderstorm, but

VII. ELECTRIC LIGHT AND HEAT
VIII. ELECTRIC POWER
IX. MINOR USES OF ELECTRICITY
X. THE WIRELESS TELEGRAPH
XI. ELECTRO-CHEMISTRY AND ELECTRO-METALLURGY
XII. ELECTRIC RAILWAYS
APPENDIX THE STORY OF ELECTRICITY. CHAPTER I.
THE ELECTRICITY OF FRICTION.

A schoolboy who rubs a stick of sealing-wax on the sleeve of his
jacket, then holds it over dusty shreds or bits of straw to see
them fly up and cling to the wax, repeats without knowing it the
fundamental experiment of electricity. In rubbing the wax on his
coat he has electrified it, and the dry dust or bits of wool are
attracted to it by reason of a mysterious process which is called
"induction."
Electricity, like fire, was probably discovered by some primeval
savage. According to Humboldt, the Indians of the Orinoco
sometimes amuse themselves by rubbing certain beans to make them
attract wisps of the wild cotton, and the custom is doubtless very
old. Certainly the ancient Greeks knew that a piece of amber had
when rubbed the property of attracting light bodies. Thales of
Miletus, wisest of the Seven Sages, and father of Greek
philosophy, explained this curious effect by the presence of a

rubbed with silk, it created sparks several inches long. The
ordinary frictional machine as now made is illustrated in figure
i, where P is a disc of plate glass mounted on a spindle and
turned by hand. Rubbers of silk R, smeared with an amalgam of
mercury and tin, to increase their efficiency, press the rim of
the plate between them as it revolves, and a brass conductor C,
insulated on glass posts, is fitted with points like the teeth of
a comb, which, as the electrified surface of the plate passes by,
collect the electricity and charge the conductor with positive
electricity. Machines of this sort have been made with plates 7
feet in diameter, and yielding sparks nearly 2 feet long.
The properties of the "electric fire," as it was now called, were
chiefly investigated by Dufay. To refine on the primitive
experiment let us replace the shreds by a pithball hung from a
support by a silk thread, as in figure 2. If we rub the glass rod
vigorously with a silk handkerchief and hold it near, the ball
will fly toward the rod. Similarly we may rub a stick of sealing
wax, a bar of sulphur, indeed, a great variety of substances, and
by this easy test we shall find them electrified. Glass rubbed
with glass will not show any sign of electrification, nor will wax
rubbed on wax; but when the rubber is of a different material to
the thing rubbed, we shall find, on using proper precautions, that
electricity is developed. In fact, the property which was once
thought peculiar to amber is found to belong to all bodies. ANY
SUBSTANCE, WHEN RUBBED WITH A DIFFERENT SUBSTANCE, BECOMES
ELECTRIFIED.
The electricity thus produced is termed frictional electricity. Of
course there are some materials, such as amber, glass, and wax,
which display the effect much better than others, and hence its
original discovery.

charged ball or indicator, they are of opposite kinds. To
distinguish the two sorts, one is called POSITIVE and the other
NEGATIVE electricity.
Further experiments with other substances will show that sometimes
the rod is negative while the rubber is positive. Thus, if we rub
the glass rod with cat's fur instead of silk, we shall find the
glass negative and the fur positive. Again, if we rub a stick of
sealing-wax with the silk handkerchief, we shall find the wax
negative and the silk positive. But in every case one is the
opposite of the other, and moreover, an equal quantity of both
sorts of electricity is developed, one kind on the rod and the
other on the rubber. Hence we conclude that EQUAL AND OPPOSITE
QUANTITIES OF ELECTRICITY ARE SIMULTANEOUSLY DEVELOPED BY
FRICTION.
If any two of the following materials be rubbed together, that
higher in the list becomes positively and the other negatively
electrified:
POSITIVE (+).
Cats' fur.
Polished glass.
Wool.
Cork, at ordinary temperature.
Coarse brown paper.
Cork, heated.
White silk.
Black silk.
Shellac.
Rough glass.
NEGATIVE (-).
The list shows that quality, as well as kind, of material affects

flows through the hand and body of the experimenter, which are
also conductors, and is lost in the ground. Glass on the other
hand, is an INSULATOR, and the electricity remains on the surface
of it. If, however, we attach a glass handle to the rod and hold
it by that whilst rubbing it, the electricity cannot then escape
to the earth, and the brass rod will attract the pith-ball.
All bodies are conductors of electricity in some degree, but they
vary so enormously in this respect that it has been found
convenient to divide them into two extreme classes conductors and
insulators. These run into each other through an intermediate
group, which are neither good conductors nor good insulators. The
following are the chief examples of these classes:
CONDUCTORS All the metals, carbon.
INTERMEDIATE (bad conductors and bad insulators) Water, aqueous
solutions, moist bodies; wood, cotton, hemp, and paper in any but
a dry atmosphere; liquid acids, rarefied gases.
INSULATORS Paraffin (solid or liquid), ozokerit, turpentine,
silk, resin, sealing-wax or shellac, india-rubber, gutta-percha,
ebonite, ivory, dry wood, dry glass or porcelain, mica, ice, air
at ordinary pressures.
It is remarkable that the best conductors of electricity, that is
to say, the substances which offer least resistance to its
passage, for instance the metals, are also the best conductors of
heat, and that insulators made red hot become conductors. Air is
an excellent insulator, and hence we are able to perform our
experiments on frictional electricity in it. We can also run bare
telegraph wires through it, by taking care to insulate them with
glass or porcelain from the wooden poles which support them above
the ground. Water, on the other hand, is a partial conductor, and
a great enemy to the storage or conveyance of electricity, from

Thus if we electrify a glass rod positively (+) and bring it near
a neutral or unelectrified brass ball, insulated on a glass
support, as in figure 6, we shall find the side of the ball next
the rod no longer neutral but negatively electrified (-), and the
side away from the rod positively electrified (+).
If we take away the rod again the ball will return to its neutral
or non-electric state, showing that the charge was temporarily
induced by the presence of the electrified rod. Again, if, as in
figure 7, we have two insulated balls touching each other, and
bring the rod up, that nearest the rod will become negative and
that farthest from it positive. It appears from these facts that
electricity has the power of disturbing or decomposing the neutral
state of a neighbouring conductor, and attracting the unlike while
it repels the like induced charge. Hence, too, it is that the
electrified amber or sealing-wax is able to attract a light straw
or pithball. The effect supplies a simple way of developing a
large amount of electricity from a small initial charge. For if in
figure 6 the positive side of the ball be connected for a moment
to earth by a conductor, its positive charge will escape, leaving
the negative on the ball, and as there is no longer an equal
positive charge to recombine with it when the exciting rod is
withdrawn, it remains as a negative charge on the ball. Similarly,
if we separate the two balls in figure 7, we gain two equal
charges one positive, the other negative. These processes have
only to be repeated by a machine in order to develop very strong
charges from a feeble source.
Faraday saw that the intervening air played a part in this action
at a distance, and proved conclusively that the value of the
induction depended on the nature of the medium between the induced
and the inducing charge. He showed, for example, that the

the floor. Muschenbroeck, eager to verify the phenomenon, repeated
the experiment, with a still more lively and convincing result.
His. nerves were shaken for two days, and he afterwards protested
that he would not suffer another shock for the whole kingdom of
France.
The Leyden jar is illustrated in figure 9, and consists in general
of a glass bottle partly coated inside and out with tinfoil F, and
having a brass knob K connecting with its internal coat. When the
charged plate or conductor of the electrophorus touches the knob
the inner foil takes a positive charge, which induces a negative
charge in the outer foil through the glass. The corresponding
positive charge induced at the same time escapes through the hand
to the ground or "earth." The inner coating is now positively and
the outer coating negatively electrified, and these two opposite
charges bind or hold each other by mutual attraction. The bottle
will therefore continue charged for a long time; in short, until
it is purposely discharged or the two electricities combine by
leakage over the surface of the glass.
To discharge the jar we need only connect the two foils by a
conductor, and thus allow the separated charges to combine. This
should be done by joining the OUTER to the INNER coat with a stout
wire, or, better still, the discharging tongs T, as shown in the
figure. Otherwise, if the tongs are first applied to the inner
coat, the operator will receive the charge through his arms and
chest in the manner of Cuneus and Muschenbroeck.
Leyden jars can be connected together in "batteries," so as to
give very powerful effects. One method is to join the inner coat
of one to the outer coat of the next. This is known as connecting
in "series," and gives a very long spark. Another method is to
join the inner coat of one to the inner coat of the next, and

Wimshurst machine. The electricity shed in the air causes the dust
and smoke to adhere by induction and settle in flakes upon the
sides of the flues. Perhaps the old remark that "smuts" or
"blacks" falling to the ground on a sultry day are a sign of
thunder is traceable to a similar action.
The most important practical result of the early experiments with
frictional electricity was Benjamin Franklin's great discovery of
the identity of lightning and the electric spark. One day in June,
1792, he went to the common at Philadelphia and flew a kite
beneath a thundercloud, taking care to insulate his body from the
cord. After a shower had wetted the string and made it a
conductor, he was able to draw sparks from it with a key and to
charge a Leyden jar. The man who had "robbed Jupiter of his
thunderbolts" became celebrated throughout the world, and
lightning rods or conductors for the protection of life and
property were soon brought out. These, in their simplest form, are
tapes or stranded wires of iron or copper attached to the walls of
the building. The lower end of the conductor is soldered to a
copper plate buried in the moist subsoil, or, if the ground is
rather dry, in a pit containing coke. Sometimes it is merely
soldered to the water mains of the house. The upper end rises
above the highest chimney, turret, or spire of the edifice, and
branches into points tipped with incorrosive metal, such as
platinum. It is usual to connect all the outside metal of the
house, such as the gutters and finials to the rod by means of
soldered joints, so as to form one continuous metallic network or
artery for the discharge.
When a thundercloud charged with electricity passes over the
ground, it induces a charge of an opposite kind upon it. The cloud
and earth with air between are analogous to the charged foils of

known as "Volta's pile." It consists of plates or discs of zinc
and copper separated by a wafer of cloth moistened with acidulated
water. When the zinc and copper are joined externally by a wire, a
CURRENT of electricity is found in the wire One pair of plates
with the liquid between makes a "couple" or element; and two or
more, built one above another in the same order of zinc, copper,
zinc, copper, make the pile. The extreme zinc and copper plates,
when joined by a wire, are found to deliver a current.
This form of the voltaic, or, as it is sometimes called, galvanic
battery, has given place to the "cell" shown in figure II, where
the two plates Z C are immersed in acidulated water within the
vessel, and connected outside by the wire W. The zinc plate has a
positive and the copper a negative charge. The positive current
flows from the zinc to the copper inside the cell and from the
copper to the zinc outside the cell, as shown by the arrows. It
thus makes a complete round, which is called the voltaic
"circuit," and if the circuit is broken anywhere it will not flow
at all. The positive electricity of the zinc appears to traverse
the liquid to the copper, from which it flows through the wire to
the zinc. The effect is that the end of the wire attached to the
copper is positive (+), and called the positive "pole" or
electrode, while the end attached to the zinc is negative (-), and
called the negative pole or electrode. "A simple and easy way to
avoid confusion as to the direction of the current, is to remember
that the POSITIVE current flows FROM the COPPER TO the ZINC at the
point of METALLIC contact." The generation of this current is
accompanied by chemical action in the cell. Experiment shows that
the mere CONTACT of dissimilar materials, such as copper and zinc,
electrifies them zinc being positive and copper negative; but
contact alone does not yield a continuous current of electricity.

electromotive force, or force which puts the electricity in
motion. The obstruction or hindrance which the electricity
overcomes in passing through its conductor is known as the
RESISTANCE. Obviously the higher the electromotive force and the
lower the resistance, the stronger will be the current in the